Incandescent cathode discharge tube



1931- K. M. VAN GESSEL 1,838,888

INCANDESCENT CATHODE DISCHARGE TUBE Filed May 28, 1927 INVENTOR KARELM.VAN GESSEL %4 glw/a A TORNEY Patented Dec. 29, 1931 UNITED j 5mmPATENT OFFICE KARIEL MARIN US VAN GEssE F.EINDHOVEN,,NETHERLAND'S,Assmma To mm CORPGRATION or .AMnnroA, VA CORPORATION or DEL W REINCANIDESGENT YCLBI'IHODE DISCHARGE TUBE a lication fi-ledgMay as, 1927,Serial no. 194, 924, and "in the Netherlands June 8', 1926.

The present invention relates to incandescentcath'ode discharge tubesand has for its object a particular cathode arrangement which maybeadvantageous in certainfcases.

\With certain types of cathodes or in particular those required to yielda definite emission at a given potential and strength of current, thewire is so long sometimes that it it is stretched out to its full lengthit canie not be introduced across the neck of the bulb. If on the otherhand the wire is bent over in a V-shaped or hairpin-shaped manner, theeffective length of the cathode is too short as in that case at eachpoint of attachment or support a length of 4 to 5 millemetres, is lostfor the emission because the heat is conducted away and only two shortpieces in the middle are heated enough to emit electrons,

According to the invention, the cathode. '20 is constructed of two ormore pieces of unequal length connected in series. The longer piece onlytakes an active part in the. emis sion, whereas the shorter piece, orpieces as the case may be, practically do not em1t because the heat isconducted away alongthe leads and supporting wires, r Q

In this case the latternon-emittingportions are preferably arrangedoutside the space enclosed by the anode and the grid so that only theeffective portion of the cathode lies in this space and thereby afavorable V influence is exercised on the characteristics of the tube. V

A single example may serve for illustration: 7

A tungsten cathode coated with barium oxide must'have a length of about30 millemetres for a current of 0.08 ampere, at a tension of 2 volts toheat the wire to incandescence. Now the greatest wire length which canbe introduced in'a stretched state through the normal bulb neck of areceiving valve is some 24 millimetres; If the 30 millimetres wire isbent into a U or V shape and supported at the ends and in the middle,the length of the two emitting portions or the ellective length of wireis 2X (152 X 5) =10 millimetres because at each point of support 5millimetres remain inactive by cooling:

nection is made i This length will hereinafter be'referred to i asuseful length.

' If, according to the invention, one end of the wire is bent over for alength of '6 millimetres or, which is better, if the two ends are bentover for a length of 3 millemetres, so that the longer portion willliavea length of 24 millimetres the allowable length which can beintroduced thru the bulb neck) the useful length metres. it i In thelatter case'tliei usefu-l length is consequently 40% greater than in thefirst case so that the inclined portion of the characteristic curve ofthe tube resulting from plotting plate current against grid potentialwill be materially greaten f is then 24 2 X 5 14 milli- The ends of thewire may be bent over at.

right angles but with a flat construction of anode and grid. itis moreadvantageous to bend the said ends so as toproducea Z; 7

It is preferable that the non-emitting part of the cathode shouldbeequally distributed at the two endsso that it would be immaterial howthe polarity of the cathode terminals is chosen. "If. the non-emittingpart isv not equally distributed at the ends, then the potentialedifilerence between grid and cathode is dependent upon which end thegrid con- If. the incandescent body consists of two parallel wires, itis possible for each of these wires to have one end bent over atrightangles and the two parts can be joinedso as to form an oblongrectangle'in which the leads engage @two oppositely disposed vertexes,or a single wire could be bent aroundfour supporting membersso-as toform a closed recg tangle with two of the supports serving as leads asin the former case. I J I The accompanying drawings show someembodiments of the invention. In the said drawingsz, V i i Figure (1shows a stem supporting a single incandescent wire,.on e endotwhichtakes no 'p'art in the emission.

H Figure 2 shows a stem with a flat arrange- V ment 'of anodeyand gridand with a sym-' metr cal construction of the single moan descent wire.c

Figure 3 shows a stem with two parallel incandescent wires joined by twoinactive portions of wire forming a rectangle.

Referring to Fig. 1 the cathode consists of two portions 1 and 2, ofwhich the greater portion 1 is arranged within the space enclosed by theanode 7 and the grid 6, at least in so far as the emitting part of thewire is concerned. As pointed out above, the heat is conducted awayalong the leads 3 and 5 and along the supporting wire 4 which carriesthe vertex of the cathode so that the temperature of the wire endsplaced outside the just mentioned space is not sufficiently raised toimpart to these ends an electronic emission of any importance.

In this unsymmetrical construction, the potential drop occurring in theportion 2 results in a material variation in the potential differencebetween the grid and cathode depending upon whether the grid 6 (ifdesired with the interposition of a biasing battery) is connected withthe lead 5 or with the lead 3.

For this reason the constructions shown in Figures 2 and 3, in whichthere is symmetry, are to be preferred.

In the construction according to Figure 2 the incandescent wire consistsof a long central piece 1 and two smaller pieces 2 and 12 of equallengths which are sharply bent over so as to produce a Z. The portion 1passes diagonally through the fiat substantially rectangular spaceenclosed by the anode 7 and the grid 6. The current is supplied alongthe leads 3 and 5 and the ends of the diagonal portion are supported bycarriers 4 and 14: respectively. Theportion 1 is the longest straightlength that can be slid through the bulb neck.

Figure 3 shows two wires similar to Figure 1 which are connected inparallel and which are united to form a rectangle. The current issupplied along the leads 3 and 5, and the two other vertexes aresupported by carriers 4 and 14. The anode 7 and the grid 6 are the sameconstruction as shown in Figure 2.

What I claim is:

1. A cathode for a discharge tube having the form of a rectangle, theportions of said cathode forming the longer sides of the rectangle beingelectron emitting portions, the shorter sides being resistances only,and leads to said cathode attached to diagonally opposite corners of therectangle.

2. In a discharge tube, a cathode consisting of a pair of filamentsconnected in par allel, said filaments being in the form of a rectangle,a press having leads passing therethru connected to the ends of thefilaments, and supports sealed in the press connected to points of thefilament intermediate of'the leads, said supports engaging diagonallyopposite corners of the filamentaryrectangle.

3. In an electron discharge tube having an anode, at least one grid anda cathode, said cathode having the form of an oblong rectanglecomprising a plurality of emitting portions in parallel, said cathodeportions each having non-emitting portions associated therewith servingas resistances only, the two narrow sides 0t said rectangle beingarranged outside the space enclosed by the anode and the grid and leadsengaging two oppositely disposed vertexes of said rectangle.

4. A cathode for a discharge tube having the form of a four-sidedgeometric figure, only one pair of opposite portions of said cathodebeing electron emitting, the other pair of opposite portions beingresistances only, and leads attached to diagonally opposite corners ofsaid four-sided cathode.

KAREL MARINU$ VAN GESSEL.

